1. Field of the Invention
The present invention relates to an electrically controlled diesel engine exhaust particle collection device.
2. Description of the Prior Art
As is well known, the exhaust of diesel engines contains large quantities of carbon particles (so-called black smoke); these carbon particles are discharged into the atmosphere through the exhaust passage and, after blowing about in the air for a long time, finally settle in the form of soot on to floors, road surfaces and clothing etc. However, it has gradually become clear that, since carbon possesses strong adsorption for other substances, various chemical substances such as carcinogen-related substances are adsorbed on to the carbon particles whilst they are free in the air, and that the entry of these into the human body when such carbon particles are breathed in by people causes cancer or diseases of the respiratory system. The diesel engines used in vehicles such as trucks and buses therefore now represent a considerable social problem as a source of environmental air pollution.
Accordingly, in order to protect the environmental air from contamination by diesel black smoke, as set out in Japanese Utility Model Application Kokai Sho.61-55114 and Japanese Utility Model Application Kokai Sho.61-84851, a black smoke collection device has been proposed wherein a black smoke removal filter consisting of metallic fibres and/or a honeycomb-shaped element or the like is arranged in the exhaust passage of a diesel engine mounted on a vehicle. However, such black smoke removal filters have the drawbacks that, when used for a long time, they get clogged up by the black smoke which they collect and pressure loss is increased.
As a means for eliminating this inconvenience, there has been proposed an electrostatic diesel particle filter which is not subject to clogging, as described in Japanese Patent Application Kokai H.2-75716. FIG. 15 is an axial cross-sectional view of the construction of the electrostatic diesel particle filter described in this publication. As shown in this Figure, in outline, this electrostatic diesel particle filter consists of: a generally tubular flow chamber 1; a corona electrode 2 consisting of a very fine linear body such as a tungsten wire stretched along the flow chamber axis in this flow chamber 1; a cylindrical isolating electrode 3 arranged facing this corona electrode 2; and a voltage source 4 whereby high voltage is applied between corona electrode 2 and isolating electrode 3. With this construction, when an exhaust gas current 5 enters flow chamber 1, carbon particles 6 contained in exhaust gas current 5 are charged up by the corona discharge and thereby deflected by the electrostatic force towards isolating electrode 3, where they are collected. As a result, clean exhaust gas current 7 whose black smoke has been reduced in amount is discharged from the diesel particle filter.
However, with such a conventional electrostatic diesel particle filter, the electrical field concentration is dispersed along the line of the corona electrode, so even though high voltage is applied, the corona discharge does not occur continuously or occurs only to a slight degree; as a result, the serious practical difficulties are produced that the exhaust particle collection capability for black smoke etc. is unstable and very small. Furthermore, since the corona electrode is a very fine linear body such as a tungsten wire, when it is mounted in a vehicle, which is subject to incessant vibration and shocks during running, there is the inconvenience that it will frequently become disconnected.